Firefox 20, currently six weeks away from a stable release, brings two nice new features to the popular open source browser — per-window private browsing and a new downloads manager.

If you don’t want to wait six weeks for the final version of Firefox 20, head on over to the Beta Channel download page and grab a pre-release copy today.

The per-window private browsing mode mirrors what you’ll find in Google’s Chrome browser and is, frankly, how it should have been all along. When you want to start a private browsing session in Firefox 20 you simply select the new “New Private Window” menu option. That will open a new window noting that Firefox will discard any history, search history, download history, web form history, cookies, or temporary internet files for sites you visit in that window. Obviously files you download and pages you bookmark will remain.

The new per-window model is much more intuitive than the old method of private browsing which put your normal browsing session on hold, hid it away somewhere and opened a new, private session. Now it’s easy to have private windows right alongside normal windows, very handy for those who, for example, need to log in to two different Gmail accounts simultaneously.

The change does have some potential consequences for Firefox add-ons using the new(ish) SDK. If you’re an add-on developer, head over to the Mozilla Add-ons blog for more details.

While Firefox might not be the first to get its new downloads interface to the web, it’s welcome nonetheless and alleviates the need to cycle through windows or hit keyboard shortcuts just to see if your downloads are done. If you want more info than is shown in the new overlay (which comes up when you click the toolbar button), the old, separate-window style downloads panel is still available.

New web technologies tend to travel a trajectory that moves from “amazing demo with fiendishly complex code”, to “very cool product feature” and finally to open source library that takes 10 seconds to add to your page. Today’s cutting edge demo is tomorrow’s jQuery plugin.

Take drag-and-drop file uploads for instance. The HTML5 File API ostensibly solves one of the most common complaints from web app users — why can’t I just drag and drop files like I do everywhere else? Well, then you could, but it wasn’t easy to build.

Dropzone.js makes it dead simple to add a drag-and-drop file uploader to any website, complete with previews of uploaded files. Dropzone also supports the traditional file-picker uploading as well; you don’t have to drag and drop.

If you’re interested, head on over to GitHub and grab the source code (obviously the plugin requires jQuery, but there is a version that will work with RequireJS as well). Also be sure to read through this Hacker News thread for some similar projects and possible alternatives for those who’d like to avoid the jQuery overhead.

For now IE 10 is an optional update, though Microsoft will be adding it as a silent background update for IE 9 users in the next few weeks. If you’ve been using the preview version released late last year, Windows Update should give you an “Important Update” message, prompting you to install the final version.

As we noted in our earlier review, IE 10 is a huge step forward for Microsoft’s oft-maligned browser, bringing much better web standards support and considerable speed improvements over IE 9. Microsoft claims Windows 7 users should see a 20 percent increase in performance over IE 9, as well as better battery life on Windows 7 laptops.

IE 10 also brings better support for modern web tools like CSS 3, HTML5 and related APIs, making life considerably easier for web developers everywhere.

Of course, while IE 10 is launching strong, Microsoft’s browser typically has a very lengthy release cycle compared to Chrome or Firefox, which both release smaller updates more frequently. Indeed, both IE alternatives are likely to see dozens of updates and improved web standards support before IE sees anything similar.

The good news is that Microsoft seems as anxious as anyone to get IE 9 users updated to IE 10 as soon as possible. Gone are the days when browser updates required active participation on the part of users. These days IE 10 will just slide into the background without so much as an EULA pop up (unless of course you want to stop the update process, which is possible). It’s a start, but until IE begins updating more frequently it will likely always be behind when it comes to web standards support.

For complete details on everything that’s new in IE 10 for Windows 7, check out the Windows blog post.

Mozilla’s “WebPhone” is one part Skype, one part Apple’s Messages and all parts web.

The demo builds on previous Mozilla efforts like the recent WebRTC video calling demo with Google, as well as the Firefox Social API demo Mozilla showed off last year (the Social API provides the glue that brings your mobile contact info into Firefox in the video above).

Aside from the cool factor, web-based calling has a potentially huge benefit for users — no more need for your phone. Mozilla’s WebPhone concept would make it possible to call from any device and the person you’re calling would still see your info.

WebPhone also makes it easy to receive calls and messages anywhere. Anyone who’s ever used Apple’s Message app knows that it’s nice to get messages on the desktop, eliminating the need to track down your phone when you’re already in front of a screen. WebPhone would make it possible to not only get messages on whichever device you’re using, but take calls as well.

Indeed what’s most surprising about Mozilla’s WebPhone demo is that AT&T and Ericsson are involved since more than anything they’re participating in a vision of the future where they are little more than pipes for sending data.

If you happen to be in Barcelona Spain for the ongoing Mobile World Congress event you can check out a live demo of WebPhone at the Mozilla booth. For now the rest of us will have to settle for the demo video above.

If advertisers gave you actual cookies while you browsed there would be less resistance. Image: scubadive67/Flickr.

Mozilla has announced that, starting with Firefox 22, the popular open source web browser will begin blocking third-party cookies by default. That means only websites you actually visit will be allowed to set cookies; advertisers on those sites will no longer be able to easily track you by setting a cookie.

While there has long been the option to block third-party cookies, by default Firefox has always allowed them.

Apple’s Safari pioneered the on-by-default approach to third-party cookies and indeed its third-party cookie policy is still more strict than what Mozilla is proposing. Google’s Chrome browser, not surprisingly, allows third-party cookies by default, as does Internet Explorer.

Mozilla developer Jonathan Mayer says the change will “more closely reflect user privacy preferences.” Mayer has set up an FAQ for users and developers, but for the most part, given that Safari has always behaved this way, the changes for developers should be minimal.

The main thing to note as a Firefox user is that the change won’t affect your current settings, nor will it remove any third-party cookies already set. So to get the benefit of the new policy you’ll need to clear out your cookies after you update.

It’s also worth noting that, while blocking third-party cookies is a step in the right direction, if you’re serious about not being tracked while you browse the web you’ll need to take stronger action, installing third-party plugins like Ghostery or DNTMe.